Early life and marriage
Carly was born and raised in Starling City. In high school, Carly was (apparently) an "ugly duckling" due to having "braces and terrible bangs" and thus not very popular with the boys. However, she grew more attractive once reaching adulthood.
At some point in her life, Carly met and married Andy Diggle, with the latter's older brother John officiating their wedding. Carly and Andy had a son, A.J., and over the course of their marriage, Carly grew close to John.
Relationship with her brother-in-law
When John brought Oliver Queen and Tommy Merlyn to the Big Belly Burger restaurant, Carly teased him about "[adopting] two white boys". She then expressed concern about the safety of his job, pointing out that being a bodyguard got her husband, John's brother, killed.
A couple nights later, Carly served John dinner at Big Belly Burger. She was suspicious about John's injured shoulder, suspecting his former job as Oliver's bodyguard to be responsible. Carly then personally met Oliver when he arrived at the restaurant. When he introduced himself, Carly quipped how she already knew who Oliver was before leaving to allow him and John to talk.
The next night at Big Belly Burger, Carly urged John to stop "moping" about quitting his job and move on to a different field, not wanting her son to lose his uncle as well. John asked Carly about her feelings regarding the fact that Andy's killer was never caught, expressing his desire to help people like he did back in the army instead of just protecting spoiled rich kids. Carly then advised him to do something he's interested in, assuring John all that mattered was if he believed in its cause. This spurred John into agreeing to join Oliver's crusade.
Carly served coffee to Oliver and Helena Bertinelli, wondering why John wasn't with them as it was nighttime in The Glades. Oliver assured Carly that Helena is "tougher than she looks". A couple nights later, Carly called John to come to Big Belly Burger and advise a depressed Oliver over his recent fallout with Helena.
Carly served Ted Gaynor a slice of cake as he reconnected with John at Big Belly Burger. She jokingly refused to give John any cake due to the latter complaining to her about his dry cleaning. Later, Carly was kidnapped and held hostage by Ted in order to blackmail John into helping him with an armored-car robbery. During the heist, John eventually shot a grenade launcher at Ted and his men, allowing Carly to escape. After Ted was killed by The Hood, Carly reunited with John as the police arrived.
When Felicity, Oliver and John were at Big Belly Burger, Oliver agreed to ask out McKenna as long as John asks out Carly. He made plans with her for dinner, although it didn't end well due to him inadvertently mentioning Andy and thus saddened her.
After John found out Deadshot was still alive, he became determined to find him and soon began to grow distant from Carly. Eventually, John realized he couldn't love Carly and hate Deadshot at the same time, leading to the couple's break up.
It has been presumed that Carly has since moved from Starling City to somewhere safer with her son. However, they still keep in touch with John.
Carly is clearly much in love with Andy, but is equally obviously attracted to John, at least by the time of the series. She has a sense of fun which has not been seen in John but brought that out in him. They both thought about Andy a lot, and that may well have prevented any real relationship between them. At work, Carly was friendly but professional with customers, and definitely didn't want John 'handling' her problems for her. She took good care of her son, and he is clearly the center of her world.
Carly seems to be quite wise as when John came to her for advice on whether or not he should do something he's not too confident he should do (being a vigilante with Oliver) without telling her unnecessary details to which she responded, it can't be wrong if he believes in it. This ultimately convinced Diggle to join Oliver as his partner.
DC's Legends of Tomorrow
- Carly and John's break-up takes place (off-screen) between Season 1 and Season 2, and Carly is not seen again after that despite being mentioned.